Certain routing logic means are already known in the art, e.g. from the paper "An extended least-hop distributed routing algorithm," by Don J. Nelson et al., IEEE Transactions on communications, Vol. 38, No 4, April 1990, pp. 520-528. Therein the routing logic means execute a routing algorithm described in part III of the paper "Nelhnet Fundamentals." The routing logic means and routing algorithm proposed in this paper are concerned with adaptive and distributed routing in a connectionless environment. Adaptive routing means that the parameters in the routing strategy are changed as a function of the network status, i.e. the transmission delay and the network topology. Distributed routing means that the routing choice is essentially made in a decentralized way, i.e. every node includes a routing logic means which determines essentially independently the next node to which a packet has to be transmitted, in order to reach a destination node with least costs e.g. with least delay. Hence, in using distributed routing, an optimal path through the packet switching network is progressively built up for every packet to be switched by letting the routing logic means in every node decide on an optimal continuation of the part of the optimal path already determined.
In the aforementioned paper the choice made by the routing logic means is based on two characteristics of the packet switching network, i.e. the transmission delay and the network topology. An optimal next node is chosen by sequentially optimizing the above two characteristics. Firstly only those next nodes are considered for which the minimal number of nodes between the latter next nodes and the destination node are below or equal to a threshold value. In one embodiment of the routing logic means of the above paper this threshold value is the minimal number of nodes between a next node and the destination node taken over all possible next nodes. Secondly, out of the remaining set of next nodes, the next node is chosen for which an estimated transmission delay to the destination node is minimal. The latter estimated delay is in this system the sum of a nodal delay for transmission to a particular next node and a destination delay which is an estimate of the minimal transmission delay from a particular next node to the destination node taken over all possible paths interconnecting the latter two nodes.
The above algorithm uses an estimate of the total delay to the destination node. This leads to signalling and processing overhead in order to distribute this delay information over a possibly very large packet switching network. Moreover, due to the dynamic nature of this delay information, and the signalling delay incurred by it, this delay information can be very inaccurate when it is used in a particular node. It can be verified that reducing the signalling and processing overhead further reduces the accuracy of the delay information whereas increasing the accuracy of the delay information results vice versa in an increase of the above mentioned overhead. The problem of this type of routing logic means thus is providing accurate information while keeping the overhead to a minimum. In any case, by taking into account also topological information a packet can be prevented from being trapped in a loop. The way in which this is accomplished however leads to a complex routing logic means needing much signalling overhead and, moreover, leads to an inflexible routing algorithm, not able for instance to adapt the relative importance of the above two criteria because they are sequentially and hence independently optimized.
An object of the present invention is to provide a routing logic means eliminating part of the above mentioned signalling overhead and flexibly routing packets based on accurate delay information.